1. Field of the Invention
The present invention relates to a porous molybdenum disilicide-based material prepared by a self-propagating high temperature synthesis (SHS) process and a method for preparing the same. More specifically, the present invention relates to a porous molybdenum disilicide-based material prepared by preheating a preform consisting of size-controlled molybdenum (Mo) powder and content-controlled silicon (Si) powder and igniting the preform to initiate self-propagating high temperature synthesis, and a method for preparing the same.
The porous molybdenum disilicide-based material thus prepared has improved mechanical durability while providing highly controlled pore size. In addition, by orienting the porous molybdenum disilicide-based material in the form of pore size gradient, porous materials used for filters with improved dirt-holding capacity can be manufactured.
2. Description of the Related Art
In general, a self-propagating high temperature synthesis process uses heat generated when starting materials are reacted with each other. The generated heat spontaneously propagates throughout the starting materials, converting them into products. Therefore, a self-propagating high temperature synthesis process is known as an economically efficient one for producing carbides, nitrides, oxides, etc., without any externally supplied energy.
Recently, special attention has been paid to a porous heating element composed of molybdenum disilicide (MoSi2) particles which has a porosity of 30˜70%. In the present invention, the porous heating element is prepared from a mixture of molybdenum powder and silicon powder using a self-propagating high temperature synthesis process.
Molybdenum disilicide (MoSi2) is a compound composed of molybdenum and silicon elements in a 1:2 molar ratio, commonly prepared using powder metallurgy.
Since materials containing molybdenum disilicide (MoSi2) as a main component form a protective surface layer which is mainly composed of SiO2 at high temperature in an oxidizing environment, they have been widely used as promising high temperature anti-oxidative heating elements.
The porous heating element prepared from molybdenum disilicide particles and remaining silicon (Si) is an electrical resistance type and has pore size capable of being freely controlled via its preparation process. The porous heating element is suitable to use for applied devices such as exhaust gas filters and heating catalyst filters which require higher porosity and excellent heating properties.
As publications describing the applications of the porous heating element, there are exemplified Korean Patent Application No. 2001-0110509 and Japanese Patent Laid-open No. Hei 11-93639. According to the publications, there is disclosed a filter for controlling fine particles in diesel exhaust which accelerate environmental pollution. In addition, Japanese Patent Laid-open No. Hei 9-42638 discloses a hot gas filter for removing dust particles from hot waste gas generated in power plants and cement plants. Furthermore, Japanese Patent Laid-open Nos. Hei 10-266827 and Hei 10-272319 disclose a technique using a porous heating element as a catalyst body.
However, no mention is made of use of a self-propagating high temperature synthesis process to prepare a porous material in these publications. Accordingly, the porous molybdenum disilicide-based heating element according to the present invention is thought to be highly inventive because its pore size and gradient property can be controlled.